Type I and Type II Alcoholism: An Update.

A commonly cited alcoholism typology, the type I-type II typology, was developed from the findings of a study of Swedish adoptees and their biological and adoptive parents. Type I alcoholism affects both men and women, requires the presence of a genetic as well as an environmental predisposition, commences later in life after years of heavy drinking, and can take on either a mild or severe form. Type II alcoholism, in contrast, affects mainly sons of male alcoholics, is influenced only weakly by environmental factors, often begins during adolescence or early adulthood, is characterized by moderate severity, and usually is associated with criminal behavior. Additional studies have demonstrated that type I and type II alcoholics also differ in characteristic personality traits (e.g., harm avoidance and novelty seeking) as well as in certain neurophysiological markers. A replication study with a second group of Swedish adoptees has confirmed many of the findings of the original adoption study.

A vast number of alcoholism 1 ty ative contributions of genetic and en coholic: Environmental factors also pologies have been developed vironmental factors to the individual's play a role in establishing a person's during the past oneandahalf susceptibility for developing the disease susceptibility to alcoholism (Kaij 1960). centuries. Equally diverse are the fac . The two sub To investigate the relative contributions tors used to distinguish between differ types identified in this typology are of genetic and environmental factors to ent alcoholism subtypes within these called type I (milieulimited) and type the development of alcoholism in more various typologies. These factors in II (malelimited) alcoholism. detail, Cloninger and colleagues (1981) clude personality characteristics, co This article reviews the findings of studied a sample of 862 male Swedish existing psychiatric disorders, gender, the Stockholm adoption study on which adoptees. This study population com and alcohol consumption patterns (for this typology was based and summarizes prised all sons born to single women in review, see the article by Babor, pp. characteristics of both type I and type Stockholm, Sweden, between 1930 and 6-14.). One frequently cited typology II alcoholics as identified in these and 1949 whose fathers were known and resulted from a study of alcoholism and subsequent analyses. Finally, the article who were adopted by nonrelatives at other relevant characteristics in a large presents data from a recent replication of an early age. The investigation also number of Swedish adoptees and their the Stockholm adoption study in a dif biological and adoptive parents. This ferent population of Swedish adoptees. C. ROBERT  included the adoptees' biological and adoptive parents. The researchers fol lowed both the adoptees and their par ents over several decades. At the time of the last data collection, the adoptees ranged in age from 23 to 43. In collecting the study data, the re searchers made use of several charac teristics of the Swedish social system that allow extensive data collection. For example, child welfare agencies record the ages, occupations, and residences of the biological and adoptive parents; the criminal registry contains records of criminal convictions; local agencies of the National Health Insurance chronicle medical diagnoses and hospitalizations; and hospital records contain informa tion about treatment for psychiatric dis orders. In addition, extensive records exist documenting a person's history of alcohol abuse. Each community has a socalled temperance board that en forces social sanctions for alcohol abuse (e.g., imposes fines) and orders and su pervises alcoholism treatment. Thus, temperance board registries document how often a person has been cited or treated for alcohol abuse. Using these data, the researchers established de tailed histories for the adoptees, their biological parents, and their adoptive parents that contained information about each subject's socioeconomic status, medical history, alcohol abuse history, and contacts with the criminal justice system.

Findings of the Stockholm Adoption Study
The researchers first investigated whether alcohol abuse in either the biological or adoptive parents increased the risk for alcohol abuse in the adopted away sons (reviewed in Sigvardsson et al. in press). The study found that alco holism in at least one birth parent in creased the son's risk of abusing alcohol (table 1), whereas alcoholism in the adoptive parents did not.
More detailed analyses of charac teristics of the biological parents and their adoptedaway sons demonstrated that the adoptees fell into two groups with respect to their alcohol abuse pat terns and birth parent characteristics predisposing them to alcoholism (Clon inger et al. 1981). The first grouptype I alcoholics-included adoptees with mild or, in some cases, severe al cohol abuse. (The severity of alcohol abuse was determined by the subject's number of registrations with the temper ance board and whether he had under gone alcoholism treatment.) A genetic predisposition (i.e., the presence of al coholism in one of the birth parents) contributed only slightly to this type of alcoholism. Any alcohol abuse in the birth parents usually was mild, required no treatment, commenced during adult hood, and was not associated with significant criminality. The adoptive environment, especially in families in which the father held a low occupa tional status (i.e., was an unskilled laborer), also contributed to the fre quency and severity of alcohol abuse in adoptees with type I alcoholism.
The second group of alcohol abusing adoptees, called type II al coholics, was characterized by more moderate alcohol abuse, compared with type I alcoholics. Predisposing factors for this type of alcoholism generally in cluded severe alcoholism in the birth father that required extensive treatment and frequently was associated with severe criminality. Both the father's alcoholism and criminality often com menced during adolescence. The birth mothers of type II alcoholics generally did not abuse alcohol. The adoptive environment appeared to contribute to the severity of type II alcoholism but did not affect its frequency. Although type II alcoholism overall was much less common among the male adoptees than type I alcoholism, men who were genetically predisposed to type II alco holism were at a significantly higher risk of becoming alcoholic themselves than men with a genetic or environmen tal predisposition to type I alcoholism.
A companion study using the same Swedish population investigated the susceptibility to alcoholism in 913 fe male adoptees with the same charac teristics as the male adoptees described previously . The study showed that, in general, alcohol abuse in the birth fathers only slightly increased the risk for alcohol abuse in adoptedaway daughters, whereas alco hol abuse in the birth mothers or in both parents increased the risk significantly (table 1). Both alcoholic fathers and mothers with certain characteristics (e.g., mild alcohol abuse, minimal crim inality, and low occupational status) in creased their adopted daughters' risk of alcohol abuse. Environmental factors (e.g., occupational status of the adoptive father) also played a small but signif icant role in determining the adopted daughters' risk for alcoholism. How ever, as with male adoptees, alcohol abuse in the adoptive parents did not influence the female adoptees' risk for alcohol abuse. In summary, the pat tern of inheritance of alcohol abuse among female adoptees corresponded to the pattern observed in type I male adoptees, indicating that type I alcohol ism can affect both men and women, whereas type II alcoholism is primarily limited to men. (In later studies, how ever, a certain proportion of female al coholics also fit the personality profile associated with type II alcoholism.) The studies' conclusion about the existence of two alcoholic subtypes generated widespread interest and stim ulated numerous additional studies, because the study had several impor tant strengths compared with previous adoption studies. First, it included a large number of subjects who had not been selected for any specific character istics other than being adoptees. Second, the adoptees and both their biological and adoptive parents were monitored for alcohol abuse and other related char acteristics during their entire lifetimes. Previous studies usually had evaluated the birth parents only up to the time of adoption, when alcoholism and other behaviors may not yet have developed. In addition, those studies frequently lacked information about the birth fathers. Third, the study had used mul tiple data sources and efficient statis tical methods to classify the subjects' alcohol abuse and determine relevant characteristics of the adoptees' genetic and environmental backgrounds.

DIFFERENCES BETWEEN TYPE I AND TYPE II ALCOHOLICS
Since the type Itype II alcoholism classification was developed, many re searchers have confirmed the findings of the original studies and have further investigated differences between the two subtypes. In these studies, the age at onset and the type of alcoholrelated problems emerged as the characteristics that most readily distinguished between the two subtypes 2 (see table 2) (Babor et al. 1992;Gilligan et al. 1988;von Knorring et al. 1987a). Type I alcohol ism developed during adulthood and generally was characterized by binge drinking (i.e., prolonged drinking bouts with default of responsibilities), inter spersed with prolonged periods of ab stinence; loss of control over drinking; excessive guilt about drinking; and rapid progression from mild to severe alcohol abuse, often accompanied by the development of alcoholic liver dis ease. Conversely, type II alcoholism generally commenced during adoles cence or early adulthood, and alcohol consumption frequently was accompa nied by fighting and arrests. In addi tion, alcohol abuse was moderately severe and frequently required treat ment, although the severity of abuse did not change over time as it did in type I alcoholism.
Other researchers detected differ ences between type I and type II alco holics not only in the age at onset and the type of alcoholrelated problems, but also in certain neurobiological markers.
For example, several studies found that compared with type I alcoholics, type II alcoholics exhibited lower activity lev els of the enzyme monoamine oxidase (MAO) (von Knorring et al. 1987b;Sullivan et al. 1990). MAO is involved in metabolizing certain brain chemicals (i.e., neurotransmitters) that mediate signal transmission among nerve cells. One neurotransmitter metabolized by MAO is serotonin. Accordingly, re duced MAO activity could indicate a reduced turnover of serotonin in the central nervous system (CNS) (Oreland and Shaskan 1983). Virkkunen and Linnoila (1990) also found that type I and type II alcoholics differed in their serotonin activities in the CNS. The serotonin levels were reduced in the brains of men with early onset alcoholism accompanied by vio lent behavior (i.e., type II alcoholics).
Type I and type II alcoholics also differed in their patterns of electrical brain waves as measured by an electro encephalogram (EEG). These differ ences existed when the subjects were resting (Cloninger 1987a), but also when they were exposed to certain stimuli. Uncommon stimuli interspersed among common stimuli (e.g., a rare green light among a sequence of red and yellow lights) elicit brain waves, called event related potentials (ERP's), that are made up of several components. A commonly studied ERP component is called P300, because it occurs about 300 millisec onds after the uncommon stimulus. Branchey and colleagues (1988) found that the P300 height (i.e., amplitude) was lower in violent alcoholics (i.e., likely corresponding to type II alco holics) than in nonviolent alcoholics (i.e., likely corresponding to type I al coholics). The P300 amplitude also was reduced in people at risk for type II alcoholism, such as sons of type II al coholics who were not alcohol depen dent themselves (Begleiter et al. 1987).
These neurobiological markers pre viously had been associated with certain stable personality traits. For example, low MAO activity was related to im pulsiveness, desire to avoid monotonous tasks, extroversion, and sensation seeking behavior (von Knorring et al. 1987a). Moreover, reduced P300 am plitudes appeared to reflect the sub jects' inability to distinguish between common and uncommon stimuli (Clon inger 1987a). Accordingly, researchers investigated whether reproducible dif ferences in personality traits existed be tween type I and type II alcoholics.
These analyses identified three heritable personality traits that could describe the prototypical characteris tics of both alcoholism subtypes: harm avoidance, novelty seeking, and reward dependence (Cloninger 1987a). The term "harm avoidance" describes whether a person is cautious, appre hensive, pessimistic, and inhibited (i.e., high harm avoidance) or confident, re laxed, optimistic, and uninhibited (i.e., low harm avoidance). People with high noveltyseeking traits are impulsive, exploratory, and distractible, whereas people with low noveltyseeking traits are rigid, reflective, and attentive to detail. Finally, a high reward depen dence describes subjects who are eager to help others, emotionally dependent, sentimental, and sensitive to social cues, whereas subjects with low re ward dependence are socially de tached, emotionally cool, practical, and tough minded.
In initial studies, type I alcoholics frequently exhibited high harm avoid ance, low novelty seeking, and high reward dependence (Cloninger 1987a), personality characteristics indicating high levels of anxiety. Type II alco holics often exhibited a reverse person ality profile, with low harm avoidance, high novelty seeking, and low reward dependence. This combination of traits also describes people with antisocial personality disorder (ASPD) (Cloninger 1987b) and is consistent with findings that type II alcoholics frequently suffer from ASPD (Gilligan et al. 1988).
The differences in personality traits between type I and type II alco holics led to a hypothesis about the underlying motivation for alcohol con sumption in the two subtypes (Clon inger 1987a). According to this theory, type I alcoholics experience a late on set of alcoholism because their high harm avoidance trait initially inhibits the initiation and frequency of drinking. After an extended period of socially encouraged drinking (e.g., drinking with coworkers at lunch), the risk of alcoholism increases, because the drinkers experience relief of their anxieties after alcohol consumption. For type II alcoholics, who primarily are characterized by high novelty seeking, alcohol use is motivated by the desire to induce euphoria. This desire, which also may lead to other drug abuse, generally begins during adolescence or early adulthood.
The personality traits of harm avoidance, novelty seeking, and re ward dependence likely are inherited independently of each other and are influenced by three brain systems that differ in the neurotransmitters they use (Cloninger 1987a). For example, the brain system for novelty seeking is pre dominantly influenced by the neuro transmitter dopamine (Cloninger 1987a). Accordingly, people who have a high novelty seeking trait are expected to react strongly to the stimulation of dopamine using (i.e., dopaminergic) nerve cells. Researchers recently confirmed this hypothesis after finding the predicted correlations between novelty seeking, plasma prolactin levels, and heritable variants of cellular components medi ating dopamine's effects (Cloninger 1996). 3 Likewise, the serotoninusing (i.e., serotonergic) nerve cells have complex effects on behavior, including facilitating harm avoidance and social cooperation (a measure of high reward dependence) .
These observations suggest certain patterns of neurotransmitter activity in different alcoholic subtypes. For exam ple, people with antisocial personality traits or type II alcoholism are expected to be uncooperative and to have low serotonergic activity in the CNS. More over, these individuals are expected to be high in novelty seeking and, there fore, low in dopaminergic CNS activ ity. In contrast, type I alcoholics, who typically are high in harm avoidance and reward dependence, are likely to be high in both dopaminergic and sero tonergic CNS activity . These predictions reflect the empirical findings that type II alcoholics consis tently exhibit high noveltyseeking traits and low cooperativeness; however, their levels of harm avoidance may vary.
Because the personality character istics are inherited independently of each other, traits such as high harm avoidance and high novelty seeking are not mutually exclusive and can occur in the same person. Accordingly, type I and type II alcoholism are not discrete diseases or separate entities; instead, alcoholism in each person is the mani festation of his or her individual combi nation of personality traits (Sigvardsson et al. in press). Thus, the type I and type II prototypes only represent the two extremes of a continuous spectrum of manifestations of alcohol abuse.

A REPLICATION STUDY IN SWEDISH ADOPTEES
Although the type Itype II distinction has become widely accepted since its inception and has stimulated a large body of research, there also has been skepticism about some of the results of the original Stockholm adoption study. For example, it seemed unlikely that one should be able to distinguish different categories of alcoholics based on the severity of their alcohol abuse (i.e., one subtype comprises alcoholics with mild or severe abuse, whereas the other subtype consists of alcoholics with moderate alcohol abuse) (Searles 1988;Littrell 1988). Similarly, it was unexpected that the genetic back grounds of mild and severe alcohol abusers should be the same, whereas the genetic background of moderate abusers differed. Although some of these criticisms already had been addressed by analyses defining ad ditional characteristics of type I and type II alcoholics, the Stockholm adoption study was not replicated independently until recently (Sigvards son et al. in press). The following sec tion summarizes the findings of this replication study, which included adop tees from Gothenburg, Sweden, and their biological and adoptive parents.
The Gothenburg study replicated the Stockholm study by including all children born to single mothers be tween 1930 and 1949 whose fathers were known and who were adopted by nonrelatives at an early age. Based on these criteria, the study evaluated 577 male and 660 female adoptees. The researchers also used the same sources to obtain comprehensive in formation about the adoptees, their biological parents, and their adoptive parents and employed the same criteria to classify the adoptees' alcohol abuse severity. The adoptees' genetic and environmental backgrounds were de termined based on criteria that had emerged during the Stockholm study (e.g., a genetic background predispos ing for type II alcoholism was charac terized by the onset of recurrent alcohol abuse during adolescence and criminal ity in the biological father; an environ mental background predisposing for severe type I alcoholism was charac terized by an adoptive father with a low occupational status).
Using these criteria, the replication study confirmed many of the original study's findings, as follows: • Among male adoptees, the risk of alcohol abuse was higher in subjects with at least one alcoholic birth par ent (24.1 percent) compared with subjects whose biological parents were not alcoholic (12.8 percent). Conversely, among female adoptees, alcohol abuse in the biological father did not increase the daughter's risk for alcohol abuse. The number of female adoptees with alcoholic mothers was too small to determine whether an alcoholic birth mother increased the daughter's risk for alcohol abuse as suggested by the Stockholm adoption study ).
• Male adoptees with both a genetic and an environmental background predisposing them to severe type I alcoholism had a higher risk of type I alcoholism than adoptees with no or with only one of these predispositions (figure 1).
• Male adoptees with a genetic back ground predisposing them to type II alcoholism had a significantly higher risk of type II alcoholism than those with no predisposition or only an environmental predisposition. The combination of both a genetic and an environmental predisposition further increased the risk for type II alcoholism ( figure 1). Conversely, a genetic and/or environmental pre disposition to type II alcoholism did not increase the adoptees' risk for type I alcoholism.
However, there also were discrep ancies between the findings of the Stockholm and Gothenburg studies. For example, in the original study, the risk for mild type I alcohol abuse in creased in male adoptees with both a type I genetic background and an en vironmental background predisposing them to mild type I alcoholism. In the replication study, however, male adop tees with these characteristics only exhibited an increased risk of severe type I alcohol abuse. The reason for this discrepancy is still unknown. It is possible that mild alcohol abuse, which is defined as a single registration with the temperance board, cannot be meas ured reliably or is not inherited con sistently. Alternatively, other inherited characteristics in the male adoptees from Gothenburg with a genetic pre disposition for type I alcoholism also might predispose them to a lower oc cupational status, which, in turn, is associated with an increased risk for severe type I alcoholism.

SUMMARY
Adoption studies investigating the relative contributions of genetic and environmental factors to a person's susceptibility to alcoholism have iden tified two alcoholism subtypes that differ in their inheritance patterns as well as in other characteristics. A pre disposition for type I alcoholism, which affects both men and women, requires the presence of a specific genetic back ground as well as certain environmental factors. This alcoholism subtype is characterized by mild or severe alcohol abuse, adult onset of the disease, a loss of control over drinking, and guilt and fear about alcohol dependence. People with this alcoholism subtype generally exhibit high harm avoidance and low noveltyseeking personality traits and drink primarily to relieve anxiety. In contrast, type II alcoholism, which oc curs more commonly in men than in women, primarily requires a genetic predisposition; environmental factors only play a minor role in its develop ment. Type II alcoholism is associated with an early onset (i.e., before age 25) of both alcohol abuse and criminal be havior and an inability to abstain from alcohol. The most common personality characteristic of type II alcoholics is high novelty seeking. These people consume alcohol primarily to induce euphoria. The differences in heritable personality characteristics and the in teraction of these characteristics with personal experiences (i.e., environmen tal factors) can explain the differences in inheritance mode, age of onset, symptoms, and course of type I and type II alcoholism.
These two alcoholism subtypes, however, represent only the prototypes or extremes of a continuous spectrum of manifestations of alcoholism. Many of the subtype characteristics (e.g., per sonality traits) are inherited indepen dently of each other, and all possible combinations of personality traits occur (Cloninger 1987b, Svrakic et al. 1993). Thus, extensive variability exists in the individual's predisposition for alcohol abuse and related behaviors . Nevertheless, high harm avoidance and high novelty seeking appear to be the traits most strongly predisposing to type I and type II alcoholism, respectively.
The validity of this typology has been confirmed in numerous inde pendent investigations, including studies of male and female twins in the United States (Pickens et al. 1991) and a replication of the original Stock holm adoption study. Although the replication study reproduced many of the findings of the original report, some discrepancies also existed. The resolution of these discrepancies will likely require further studies in addi tional subject populations. ■